Uncertainty in antimicrobial susceptibility testing of Moraxella catarrhalis

Moraxella catarrhalis is a Gram-negative diplococcus and part of the normal flora of the upper respiratory tract with other bacteria such as the pneumococcus and Haemophilus influenzae. It commonly causes acute otitis media in children and serious lower respiratory tract infection in elderly and immunocompromised patients.¹

                The agar disk diffusion method for antibiotic susceptibility testing (AST) is currently used as the official method of AST in many clinical laboratories, due to its simple and well-standardised procedure.² In 2019, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) introduced a new concept called the Area of Technical Uncertainty (ATU) in AST.³

                This study aimed to determine whether or not uncertainty of measurement affects the interpretation of an antimicrobial susceptibility testing measurement of M. catarrhalis. Its objectives are to i) determine the area of uncertainty of clinical isolates of M. catarrhalis against cefixime, cefotaxime, ceftriaxone, erythromycin and tetracycline; ii) assess the EUCAST 15-minute rule of AST by increasing it to two hours for each time interval; iii) assess the measurement of antibiotic susceptibility testing of M. catarrhalis using different agar types; and iv) examine the effects of variation of agar depth on the measurement of antibiotic susceptibility testing of M. catarrhalis.